The plastic extrusion art has developed into a complex mechanical and chemical science; and consequently the relative expense in operations thereof have become an onerous burden. The complexities of the machinery involved are generally matched significantly in direct proportion to the energy requirement involved. In addition to the problems of encountering relatively complex machinery in the extrusion art, there is a vast deficiency in existing extrusion equipment to handle the problem of extruding variegated plastic waste products and used plastic materials so as to be able to recycle such materials back into a usable raw material form for further processing. The following discussion of the background of the prior art set forth below will entail a discussion of these problems as they relate to the general objects and purposes for which the subject invention has been conceived.
The conventional plastic extruder is basically comprised of a supportive frame member; a hopper which functions to feed the raw plastic material into the extruder unit; a cylindrical barrel member containing a screw device serving to both mix the plastic and move the plastic product to the extruder outlet; power means to drive the screw element; heating means to heat the plastic material in the barrel; and means at the end of the barrel to serve as the extrusion outlet. Each of these elements, as will be discussed, yield special cost, operational, and rigidity of usage problems in the extruding process, which do not yield the desired mechanical flexibility in handling the problem of extruding many different forms of plastic materials.
The supportive frame member in either a vertical or horizontal extruder is usually a cast iron member. Its size and strength will obviously depend largely on the complexity and amount of equipment appended to the basic extrusion unit. As in other areas of machinery usage, the usage of lighter and less complex extrusion equipment would yield the need for less bulky frame members. Thus, any conception in the extrusion art which results in lighter extrusion equipment requires also a lighter frame member thus reducing initial capital outlays.
The feed element in the conventional extrusion machine is most usually a simplistic sheet metal enclosure adapted to vertically feed the raw plastic into the barrel member. Frequently, the orifice of the feed element leading to the extrusion barrel is relatively small, although not in all cases. When this latter situation is encountered there is a relatively larger heat requirement in order to move the plastic through the orifice into the barrel. In some instances this latter difficulty is alleviated by providing the feed element with a self contained heater unit which serves to preheat the plastic material before it enters the barrel member. Moreover, in some polymer extrusion processes, individual polymer batches are preheated separately before being fed into the barrel member. More recently, the feed hopper element has also been equipped with drying units that circulate dehumidified air in order to prepare the plastic for optimal processing and reduce thereby initial heating requirements.
It is obvious from the foregoing, at least to one who has had some familiarity with the plastic extrusion art that any such complexity in the feeder unit or its operation causes higher operational and capital costs in the extrusion process. In this consideration, it is important, and indeed critical, not to overlook one of the most essential steps in the extrusion process, that is the need to render the plastic pliable into a semi-molten amorphous state in order that it may be readily worked and extruded at a sufficiently warm, but not too high, temperature at the extrusion outlet. Any solution to the problem within this necessary parameter of of delivering the plastic material to the extrusion outlet in the optimal state, which concurrently requires a minimal amount of heat or energy, would obviously produce operational efficiencies which by itself would yield inventive distinction over the prior art. Specifically, the saving of energy is a particularly significant criteria in ascertaining one of the steps of inventiveness.
As mentioned above, the core of the conventional extruder machine is the barrel member which encases a stoker-like screw member serving to both churn the amorphous plastic and move it to the end of the extruder for the final extrusion process. The usual extruder barrel length varies from twenty to thirty times its diameter, and obviously such sizes cause relative inefficiency in operational performance.
In addition, because of the high internal pressures encountered in an extruder barrel, e.g. 50 to 400 atmospheres, it is essential that the barrel be constructed of a heavy steel material. Thus, one can see that large quantities of metal are required in the usual barrel construction. Yet another peripheral requirement of the extreme barrel pressures is that the barrel member must be appropriately vented along the length, leading to inefficient heat losses. In the more complex extruders the plastic is softened and melted in the barrel member to a more pliable state. As part of this first stage the plastic is mixed, and then immediately passed into a channeled zone open to the atmosphere or a vacuum in order to vent the hot gases produced. Thereupon the plastic is then moved to a second stage and ultimately delivered to the extrusion outlet to form the final product.
Thus, as can be seen above, all the extrusion units require a method of heating the plastic as it moves through the barrel, but with such venting of hot gases heat losses become considerable. Most such units are electrically heated to temperatures in the range of 300 degrees centigrade. One of the more frequently encountered heaters of the latter type are band-type electrical resistor heaters situated circumferentially around the barrel. Others utilize an induction heating process as a means of heating the plastic. Moreover, contemporary extrusion units are constructed to capitalize on the heat generated by the internal friction of the plastic to supplement the extreme heat input. In the more complex extrusion equipment, a cooling system such as the venting system discussed above, must be utilized because of the heat produced by the high speed of the extrusion equipment. The difficulty with the presence of the higher degree of heat is that within higher temperature ranges there is risk that the polymer may suffer degradation. This overview of the barrel function of a conventional extruder reveals inherent operational inefficiencies, particularly from the aspect of energy usage. Furthermore, it is readily ascertainable that the rigidity of the barrel structure restricts the types, quantities, and compositional makeup of the plastic material to be extruded. More specifically, an extruder of conventional cast is usually structurally limited to handle only one type of plastic material.
It is this dual problem of energy usage inefficiency and the limited adaptability of conventional extrusion equipment to which this invention is directed. More specifically, this invention has been produced to overcome the high energy requirements that are encountered in the operation of a conventional extruder, whether of the blow molding or injection molding type. As previously discussed, in this area of energy shortages, such projected goals are of significant importance to society at large. It is most important that utilization be made of manufacturing processes that use efficient machinery. Another disadvantage of the conventional extrusion machinery discussed above, is that such machines are generally adapted only to extrude raw plastic of only one type or composition. With today's emphasis on saving and recycling waste materials back into usable products, need has arisen for means to mold plastic materials of variegated forms into usable raw material for further processing back into final products. In particular, many waste products that arrive at a processing facility exist and are contained in such various forms that a standard extrusion machine is incapable of handling a variety of different forms and compositions of plastic. Most such standard extruders are adapted to extrude a plastic substance of uniform composition without impurities for molding into a final product. This invention is thus a device capable of handling variegated plastic waste products so that they can be extruded into a fairly uniform and impurity-free plastic material that can be used for further processing into final products, which may require further extrusion into a final product. This invention is thus in essence a pre-extrusion processor.
Therefore, the objects of this invention are as follows:
It is an object of this invention to provide an improved plastic extrusion machine;
It is a further object of this invention to provide a plastic extrusion machine which uses relatively little energy and heat in its operation;
Still another object of this invention is to provide an improved machine for converting and eventually extruding large and miscellaneous chunks of plastic which are of variable size, variable density, and bulkiness;
It is still another object of this invention to provide a more efficient plastic extrusion machine;
Yet another object of the invention is to provide an improved plastic extrusion process;
It is also an object of this invention to provide a versatile and flexible plastic conversion and extruding machine;
Still another object of this invention is to provide an extrusion machine using gravitational forces to aid the extrusion process;
Another object of this invention is to provide a plastic extrusion machine capable of facilitating the recycling of waste or used plastic materials into usable form.
Another object of this invention is to provide an extrusion machine which is capable of extruding plastic materials of various sizes and shapes into continuous strands for further usage.